Earth has been habitable for 4.3 billion years, and the earliest rock record indicates the presence of a microbial biosphere by at least 3.4 billion years ago—and disputably earlier. Possible traces of life can be morphological or chemical but abiotic processes that mimic or alter them, or subsequent contamination, may challenge their interpretation. Advances in micro- and nanoscale analyses, as well as experimental approaches, are improving the characterization of these biosignatures and constraining abiotic processes, when combined with the geological context. Reassessing the evidence of early life is challenging, but essential and timely in the quest to understand the origin and evolution of life, both on Earth and beyond.
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This research was supported by the European Research Council StG ELiTE FP7/308074 and the Belgian FRS-FNRS-FWO Excellence of Science project ET-HOME. N. Butterfield, J. Cosmidis, C. Demoulin, A. H. Knoll and K. Lepot are acknowledged for providing some of the images. I thank many colleagues for fruitful discussions over the years, and I apologize for all the work that could not be cited, owing to limitations of space.
The author declares no competing interests.
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Peer review information Nature thanks Shuhai Xiao and the other anonymous reviewer(s) for their contribution to the peer review of this work.
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Javaux, E.J. Challenges in evidencing the earliest traces of life. Nature 572, 451–460 (2019). https://doi.org/10.1038/s41586-019-1436-4
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